In adhering a rubber composition and a fiber material together, it has been the common practice to treat the fiber material with a resorcinol resin-formalin-rubber latex (RFL) liquid or, for improved adhesion, to treat the fiber material with an epoxy compound or isocyanate compound. A basic dry bonding (HRH) method is also used, in which a diene rubber is admixed with hydrated white carbon [hydrous silica (SiO.sub.2 -(NH.sub.2 O))], either resorcinol or a resorcinol derivative, and a methylene donor such as hexamethylenetetramine. The HRH method is described in Rubber Chemistry and Technology, Vol. 49, p 752. The above common practices produce an adhesion surface on the fiber material. The initial adhesion can be good. However, after thermal aging adhesion declines significantly or adhesive function can to be lost due to adhesion surface hardening due to heat.
Organic peroxides have recently been used in place of sulfur or sulfur compounds to crosslink rubber for the purpose of improving the heat endurance of the crosslinked rubber. However, when using the organic peroxide for crosslinking, treatment of the fibers with RFL liquid causes the resorcinol resin to be reacted and hardened by the organic peroxide, resulting in significant deterioration of the adhesion surface and fiber material. There is significant deterioration of the adhesion surface and fiber material when the organic peroxide is used in the presence of the epoxy compound or isocyanate compound. In the presence of the organic peroxide, the HRH method is also faulty in that it fails to offer sufficient initial adhesion.
There is a desire for a rubber composition having good adhesion to fiber materials after crosslinking, wherein it is unnecessary to treat the fiber material with a RFL liquid, an epoxy compound, an isocyanate compound or the HRH method to adhere the rubber composition and the fiber material, adhesion after crosslinking is good and adhesion after thermal aging is also good. The rubber composition should be applicable to ordinary rubber products such as belts, tires and hoses.